The present invention relates to solid state optical waveguides which can be used for a number of applications requiring the transmission of optical signals. Furthermore, the invention may be used to form closed loop optical resonators.
Optical waveguides have become increasingly popular for a number of purposes including optical communications, optical signal processing, optical interconnects, optical sensing and many other applications where optical signals need to be transmitted from one point to another. Furthermore, optical waveguides are being investigated for use as resonant sensing elements in rotation measuring instruments.
In the field of optical waveguides propagation loss within the waveguide is a primary concern. The amount of propagation loss will effect the operability and efficiency of the waveguide. Generally, optical waveguides are designed to be low loss devices. However it is advantageous to further minimize all propagation losses within the waveguide. Any propagation loss within the waveguide degrades light wave transmission because the signals being transmitted will attenuate over distances. This creates the need for ultra low loss waveguides which are capable of transmitting signals over relatively large distances. Furthermore, ultra low loss waveguides will be beneficial to many other waveguide applications.
Optical waveguides can be fabricated using a wide variety of techniques, including deposition, diffusion, ion-exchange, and the use of nonlinear optical effects. One approach uses thin film deposition in which the optical waveguides are fabricated by depositing material upon a substrate and then etching or carving away unwanted portions to create a channel waveguide. Many methods of depositing material for waveguide fabrication have been attempted. Some attempts have met with success while others have continually encountered the problems of propagation loss. Examples of the deposition techniques used to fabricate waveguides include magnetron sputtering and chemical vapor deposition.
The methods by which a waveguide is fabricated can greatly effect its characteristics. A number of factors can contribute to the efficiency and performance of the deposited waveguide. First, the material making up the waveguide should be homogeneous and free of impurities. Any impurities within the material will cause an increase in propagation loss through scattering and absorption, while inhomogeneities will cause scattering loss. Additionally, it is essential that the dimensions of the waveguide be controlled with high uniformity over large areas. Any variations in the waveguide dimensions will cause additional propagation loss due to changes in the optical mode structure along the waveguide.
During fabrication excess handling can cause impurities and irregularities in the waveguides. It is desirable to fabricate the waveguides using a process which requires little, if any, physical handling of the waveguides, thus reducing the possibility of creating impurities and irregularities.